As women live longer and have fewer children, they are becoming taller and slimmer, study finds

(26 April 2013)

A Durham University study of people living in rural Gambia shows that the modern-day “demographic transition” towards living longer and having fewer children may also lead women to be taller and slimmer.

The findings in Gambia, published today in the journal Current Biology, may have relevance around the globe.

Dr Ian Rickard, Lecturer in the Department of Anthropology, worked with Alexandre Courtiol of the Leibniz Institute for Zoo and Wildlife Research in Germany to show that changes in mortality and fertility rates in Gambia, likely related to improvements in medical care since a clinic opened there in 1974, have changed the way that natural selection acts on body size.

For the study, data was collected over a 55-year period (1956–2010) by the UK Medical Research Council on thousands of women from two rural villages in the West Kiang district of Gambia. Over the time period, those communities experienced significant demographic shifts—from high mortality and fertility rates to rapidly declining ones. The researchers also had thorough data on the height and weight of the women.

Their analysis shows that the demographic transition influenced directional selection on women’s height and body mass index (BMI). Selection initially favoured short women with high BMI values but shifted over time to favour tall women with low BMI values.

Dr Ian Rickard said: “This is a reminder that declines in mortality rates do not necessarily mean that evolution stops, but that it changes.

“Our results are important because the majority of human populations have either recently undergone, or are currently undergoing, a demographic transition from high to low fertility and mortality rates. Therefore the temporal dynamics of the evolutionary processes revealed here may reflect the shifts in evolutionary pressures being experienced by human societies generally.”

Alexandre Courtiol said: “Although we cannot tell directly, it may be due to health care improvements changing which women were more or less likely to reproduce.”

Rickard and Courtiol collaborated with researchers at the Medical Research Council’s International Nutrition Group at the London School of Hygiene & Tropical Medicine on this study.